Many devices and machines use drive shafts to run various power take-off devices. For instance, in turret machines, such as those used to make paper cups and the like, drive shafts run main turrets on which cups are formed, various delivery turrets, and numerous mechanical work stations that perform a variety of cup forming operations. The power take-off devices are connected to the drive shaft by mechanisms such as an indexing roller gear cam, drive sprocket or gear.
The drive shaft of these machines experiences variable torque at each torque load point where a power take-off device is connected to the shaft. This poses a substantial problem under many operating conditions. For instance, where an indexing turret is driven by a roller gear cam mounted on the drive shaft, a varying torque is placed on the shaft each time the turret is accelerated and decelerated during indexing from one position to the next. This can cause an angular twisting of the drive shaft which leads to fatigue and wear on both the drive shaft and the driven components.
Twisting of the shaft also leads to inaccurate operation of the various driven components. This inaccuracy can cause formation of less desirable products. For instance, if a shaft is flexing angularly, portions of the shaft are momentarily running at different angular velocities than other portions of the shaft making it difficult to precisely time the various power take-off devices and work stations. As machines are run at higher and higher speeds, this twisting of shafts and the resultant variation in angular speed along the shaft makes precise alignment of components and timing of procedures increasingly more difficult.
Shaft spring-back after a heavy load or torque is released can also occur. For example, when a heavy turret is accelerated during the first segment of an indexing operation, an increased torque is imposed on the drive shaft. However, after the acceleration is completed and the heavy torque is reduced or eliminated, the shaft tends to spring back and actually twist in the opposite angular direction, again leading to uneven angular velocities throughout the length of the shaft. Nearly any driven component which places varying torques on a shaft will cause twisting and spring-back thereby limiting the accuracy of the driven components. This problem, of course, is amplified when the speed of operation is increased and the resultant torques and spring-backs are also increased.
It would be advantageous to balance the energy absorbed by a given shaft. In such a system, torques acting on a shaft would be counterbalanced to minimize twisting of the shaft and to stabilize the angular velocity of the shaft along its entire length.